The Early Manifest Glaucoma Trial (EMGT) is the first large randomized, controlled clinical trial to evaluate the effect of lowering the intraocular pressure (IOP) on the progression of newly detected open-angle glaucoma. As such, it is an extremely important study designed to address a major unresolved issue in ophthalmology. The primary aim of the EMGT is to compare the effect of immediate therapy to lower the IOP (laser trabeculoplasty and betaxolol) versus late or no treatment on the progression of newly detected open-angle glaucoma, as measured by increasing visual field loss or optic disc changes. The primary aim will be achieved by conducting a randomized clinical trial of 300 patients that will compare glaucoma progression in initially treated vs untreated patients with newly detected open-angle glaucoma. This comparison will allow quantification of the effect of immediate IOP-lowering treatment on progression during the followup period. Patients will be followed every three months until the development of glaucoma progression endpoints for a minimum of four years. Secondary aims are to: 1) determine the extent of IOP reduction attained by treatment; 2) explore the factors that may Influence progression; and, 3) describe the natural history of newly detected glaucoma. The proposed EMGT is a collaborative effort that involves a Clinical Center (CC) in Malmo, Sweden, a Disc Photography Reading Center in Lund both at the University of Lund, Sweden, a Data Center (DC) at the State University of New York, Stony Brook, NY and the National Eye Institute. The study originated from a proposal prepared by the CC that was approved and funded by the Swedish Medical Research Council. Funding was limited to a study of 200 patients and involved only the CC. The present collaboration involves several design changes (e.g., increase in study power from 70% to 90% and sample size to 300 patients, incorporation of rigorous clinical trial methodology, inclusion of an independent DC and a Data Safety and Monitoring Committee) to strengthen the original study plan and enhance interpretation of EMGT results. The DC will be involved in all aspects of the study design, implementation and analysis. The specific responsibilities of the DC are to: 1) serve as a collaborating partner in the EMGT and provide epidemiologic and biostatistical input to the organization, design, conduct and analysis of the trial; 2) collaborate in the development and distribution of forms, documents and protocols; 3) develop, implement and maintain quality assurance procedures for all aspects of the study; 4) develop and monitor the randomization process; 5) be responsible for data management, processing and analysis; 6) prepare reports for study committees to monitor recruitment, data collection, adverse effects, endpoints and data quality; 7) coordinate and document study meetings and communications between centers; and 8) collaborate in preparing publications of the results.